Photonic antenna array with tapered fiber ends
A photonic antenna array includes: a plurality of tapered fiber ends; and a support plate. Each tapered fiber end of the plurality of tapered fiber ends corresponds to a respective fiber of a plurality of fibers. A portion of each of the plurality of fibers is run through the support plate. A fiber core diameter at a tapered end point of a respective tapered fiber end of the plurality of tapered fiber ends has a first diameter. A fiber core diameter at a non-tapered portion of the respective fiber corresponding to the respective tapered fiber end has a second diameter. The first diameter is smaller than the second diameter. The respective tapered fiber end is configured to provide a mode field diameter larger than a diameter of the non-tapered portion of the respective fiber corresponding to the respective tapered fiber end.
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This application claims priority to U.S. Provisional Patent Application No. 62/776,299, filed Dec. 6, 2018, which is incorporated by reference herein in its entirety.
BACKGROUNDConventional satellite communications utilize radiofrequency (RF) communications. However, the frequency ranges used for RF communications are becoming more and more crowded and are bandwidth-limited. Optical satellite communications using lasers are being explored, with some optical satellite communication systems having been tested. However, existing optical satellite communication systems suffer from many drawbacks, such as reliance upon heavy equipment, complicated and expensive system configurations, low telescope slew rate, low reliability, and/or inability to handle high power (e.g., in the kilowatt (kW) range or higher).
Optical systems are also used in directed energy applications, which are typically much higher power than communications applications (e.g., on the order of hundreds of kW versus low power on the order of ˜10 W for communications). Conventional directed energy systems suffer from many of the same drawbacks as conventional optical satellite communication systems.
In particular, conventional approaches to optical communication systems and directed energy systems typically either use a tiling approach (which suffers from low efficiency and output intensity) or a diffractive approach (which suffers from low reliability due to all of the system light being directed through single components).
Additionally, liquid crystal technology is also being explored, but liquid crystal approaches also have various drawbacks, such as low scalability.
SUMMARYIn an exemplary embodiment, the present application provides a photonic antenna array. The photonic antenna array includes: a plurality of tapered fiber ends, wherein each tapered fiber end of the plurality of tapered fiber ends corresponds to a respective fiber of a plurality of fibers; and a support plate, wherein a portion of each of the plurality of fibers is run through the support plate; wherein a fiber core diameter at a tapered end point of a respective tapered fiber end of the plurality of tapered fiber ends has a first diameter, wherein a fiber core diameter at a non-tapered portion of the respective fiber corresponding to the respective tapered fiber end has a second diameter, and wherein the first diameter is smaller than the second diameter; and wherein the respective tapered fiber end is configured to provide a mode field diameter larger than a diameter of the non-tapered portion of the respective fiber corresponding to the respective tapered fiber end.
In another exemplary embodiment, the present application provides a light output system. The light output system includes: a transmitter system comprising a plurality of laser channels and a plurality of phase shifters; a photonic antenna array comprising a plurality of tapered fiber ends, wherein each tapered fiber end is configured to output a beam corresponding to a respective laser channel of the plurality of laser channels; and a controller, wherein the controller is configured to control the plurality of phase shifters to provide phased array beam steering with respect to an aggregate output provided by the photonic antenna array.
In yet another exemplary embodiment, the present application provides a fiber. The fiber includes: a clad having a clad diameter; a core having a core diameter; a non-tapered portion, wherein in the non-tapered portion of the fiber, the clad diameter is a non-tapered clad diameter and the core diameter is a non-tapered core diameter; and a tapered fiber end, wherein the tapered fiber end comprises a tapered portion of the fiber terminating in a taper point at an end of the fiber, wherein in the tapered portion of the fiber, the clad diameter decreases to be smaller than the non-tapered clad diameter and the core diameter decreases to be smaller than the non-tapered core diameter, and wherein at the taper point, the core diameter is less than 5 μm; wherein the tapered portion of the fiber is configured to output a collimated light beam having a mode field diameter larger than the non-tapered clad diameter.
Exemplary embodiments of the present application provide a photonic antenna array that allows for vastly improved optical satellite communication systems and directed energy systems to be achieved relative to existing approaches. Optical communication systems incorporating photonic antenna arrays of exemplary embodiments of the present application can be compact, lightweight and accurately steerable while still providing high-speed and highly power-efficient communications, thereby supporting gigabit level and higher data rates for spacecraft having numerous and complex sensors. Additionally, directed energy systems including photonic antenna arrays of exemplary embodiments of the present application can also be compact, lightweight and accurately steerable while providing highly efficient directed energy output beams at high power. For example, exemplary embodiments of the present application are able to achieve a far field central lobe efficiency of almost 100%, whereas conventional tiling approaches are only able to achieve 60-70%. At the same time, exemplary embodiments of the present application achieve the reliability of tiling approaches based on no single optical element of the system seeing the whole power of the system.
The photonic antenna array may include densely packed photonic antennas, wherein each photonic antenna corresponds to a tapered fiber end. Because each tapered fiber end is tapered in such a way as to provide a large mode field diameter (MFD) greater than the diameter of the fiber, the photonic antenna array is able to achieve high fill factor and high far field combining efficiency, so as to be operable as a phased array capable of fast slewing and fine beam steering. These photonic antenna arrays are thus highly advantageous for use in low earth orbit (LEO)-to-LEO optical links, LEO-to-geocentric orbit (GEO) optical links, and LEO-to-ground optical links, as well as in other types of applications such as directed energy applications.
The photonic antenna array may further include positioners (including, for example, lead zirconate titanate (PZT) transducers) corresponding to the respective photonic antennas to provide additional electronic beam steering functionality by physically pointing the photonic antennas within a corresponding range of motion. Through phased array operation and/or physical pointing, precise and accurate beam steering can be achieved. The range of angles achievable via phased array operation may be similar to the range of angles achievable through RF phased arrays (e.g., ˜120 degrees), and in a system that is both capable of phased array operation and which has positioners, the range of angles achievable for beam steering is enhanced even more (see
Additionally, the photonic antenna array may have a thin support plate and, due to being fiber-fed and being lightweight, may be arranged as a conformal antenna aperture mounted on the side of a spacecraft.
Each respective laser channel has corresponding components for generating a desired output forming a portion of the overall output beam. For example, in an exemplary embodiment, the transmitter system 11 include a respective laser for each laser channel. With such a configuration, and due to the multi-fiber feed, very high powers can be synthesized through the use of multiple small sources such as vertical cavity surface emitting lasers (VCSELs) or fiber-amplified sources. In another exemplary embodiment, the transmitter system 11 may include less than x lasers—for example, multiple lasers each having multiple laser channels or one laser having x laser channels. In one exemplary implementation, the transmitter system 11 include multiple VCSELs phase-locked to a single local oscillator. In another exemplary implementation, the transmitter system 11 include a single VCSEL split into multiple channels, with each channel having a respective phase shifter for phased array beam steering (this may be useful, for example, in low power communications). The number of laser channels used in a system may be based on a desired final divergence (or “aperture”) and overall power output. It will be appreciated that each laser channel depicted in
A controller 14 of the system (which may be a single controller or which may include multiple separate controller components), provides various control functions with respect to the components of the one or more laser channels, the phase shifters 12, and the positioners 25. The controller 14 may actuate the positioners 25 to provide “coarse” steering for the plurality of tapered fiber ends 9 of the photonic antenna array 10 (by physically pointing the tapered fiber ends 9 in a desired direction), and may further control the phase shifters 12 to impart respective phase shifts for each of the respective laser channels to further provide “fine” steering for light output from the plurality of tapered fiber ends 9 of the photonic antenna array 10. The amount of phased array “fine” steering provided by the phase shifters 12 is based on phase relations between the respective outputs at respective photonic antennas of the photonic antenna array 10. The controller 14 may also utilize the phase shifters 12 to provide array phase control to account for path length differences in the fibers (in addition to adding phase offsets for beam steering).
It will be appreciated that the positioners 25 may be optional. In an exemplary embodiment without the positioners 25, electronic beam steering is provided through the phased array operation of the phase shifters 12, which provides for beam steering up through an angle corresponding to beam divergence (the divergence of the single beam corresponds to the exit aperture via diffraction, and for multiple coherently combined beams, the overall divergence is determined by the width of the entire aperture). In another exemplary embodiment, the positioners 25 are included, and together with the electronic beam steering provided through the phase shifters 12, the overall steering angle is increased beyond the angle corresponding to beam divergence.
In communications applications (such as for optical satellite communications), the controller 14 may further provide for modulation of data onto the light carried through the respective fibers, for example, by directly modulating the intensity of the output on each of the laser channels. Alternatively, the controller 14 may cooperate with one or more modulators (such as phase modulators or polarization modulators) of the respective laser channels to modulate another characteristic of the light. In an exemplary embodiment, a type of modulation known as LOCKSET modulation may be used. In directed energy applications, data modulation would not be needed, and the transmitter system 11 may instead be referred to as a directed energy output system.
The controller 14 may also provide for monitoring and control of phase and polarization to facilitate coherent combining with respect to overlapping light beams, for example, using similar techniques as those performed in RF radar systems, in LOCKSET systems, and/or coherently combined laser systems for directed energy applications.
The controller 14 may include hardware, software, firmware or a combination thereof. For example, the controller 14 may include one or more processors or chips with one or more non-transitory memories associated therewith for storing processor-executable instructions. Control operations performed by the controller 14 may be executed using the hardware, software, firmware or a combination thereof. The controller 14 may further include a user interface through which a user can provide control commands, or the controller 14 may be in communication with a computing device having a user interface through which a user can provide control commands.
It will be appreciated that the systems shown in
It will further be appreciated that various types of fiber, various lengths of fiber, and various different photonic antenna array shapes and dimensions may be used. For example, although
For example, in an exemplary directed energy application, an overall output aperture of a photonic antenna array may be approximately 12″ (˜30 cm), with each photonic antenna of the photonic antenna array having an individual aperture of about 1 cm, further with 100+ (e.g., 500-1000) fibers being provided (corresponding to 100+ photonic antennas) with 100+ corresponding laser channels having a total power output of >1 MW. To provide another example, in an exemplary communications application, the overall output aperture of a photonic antenna array may be approximately 4-8″. In other exemplary applications, such as for telescopes, the overall output aperture of the photonic antenna array can be further increased to provide a larger range of steering capabilities.
With regard to the slope of the taper, exemplary embodiments of the present application may utilize an “adiabatic” or near-adiabatic taper (e.g., over a length of 5-30 mm) which provides for a gentle enough slope that provides high efficiency through the taper (i.e., conserving brightness by avoiding undesirable scattering and back-reflections). In certain exemplary embodiments, the taper slope may satisfy the adiabatic condition or be more gradual (i.e., less steep) than a slope that would satisfy the adiabatic condition. In other exemplary embodiments, the taper slope may be steeper than a slope that would satisfy the adiabatic condition, but still be gradual enough to provide high efficiency (e.g., less than 10% loss).
With regard to fiber length, an exemplary fiber length between a laser channel and a photonic antenna array may be, for example, 2-3 meters, but it will be appreciated that there is no particular length requirement and other fiber lengths may be used. With regard to fiber type and diameter, virtually any type of fiber may be used, but certain types of fiber and/or certain dimensions of fiber may be suitable for certain application. An example of a fiber that may be used in a communications application is standard telecom fiber having a 6 μm non-tapered core diameter and a 125 μm non-tapered clad diameter, with a taper length of, for example, about 25 mm to 200 mm down to a taper point having an overall diameter (including clad and core) of 10 μm or less or 1 μm or less. An example of a fiber that may be used in a directed energy application includes a large mode area (LMA) fiber having a non-tapered core diameter of 20 μm or more.
Generally speaking,
As will be discussed below in connection with
The light beams exiting the fibers 2 corresponding to the MFDs 22 are collimated, such that the overall output of the photonic antenna array is collimated, and also such that individual tapered fiber ends 2 may be used as individual fiber collimators. Thus, for example, there are also exemplary embodiments of the present application (outside of the context of photonic antenna arrays) in which one or more tapered fiber ends are used to provide for collimation of light carried by one or more respective fiber(s).
Because light travels outside of the fiber 2 to form the MFD 22, the light is affected by the index of refraction of the medium outside of the fiber 2. In certain exemplary embodiments, as shown in
Alternatively, in certain exemplary embodiments, the medium outside the fiber may simply be air (for which the index of refraction is n=1), in which case the photonic antenna array might not include index material 34 and the outer wall surrounding the index material 34. If the medium outside the fiber is air, the amount of MFD expansion would be less than the amount of MFD expansion for an index material 34 having an index of refraction of n>1.
Due to the working principles of the photonic antennas as shown in
As depicted and discussed above with respect to
In exemplary embodiments of the present application, beam steering may be achieved through actuation of the positioners 25 alone, through phased array operation alone, or through a combination of actuation of the positioners 25 and phased array operation. By combining phased array operation and physical tilting through actuation of the positioners 25 (e.g., as shown in
The tilting capability provided by the tilt transducer 44 allows for each respective positioner 25 to tilt a corresponding tapered fiber end in a desired direction over a wide range of angles. The amount (degree) and direction of tilt provided by each respective positioner 25 may be controlled based on control signals supplied by a controller (e.g., by the controller 14 in electrical communication with the respective positioners 25 of the photonic antenna array 10).
Further, the piston motion capability provided by the piston transducer 40 may be used to account for flex in the photonic antenna array, to offset differences in fiber lengths, and/or for phased array operation. For example, in addition to or instead of relying on phase shifters 12 as depicted in
It will be appreciated that although the steering capabilities associated with phased array operation and/or physical tilting of the tapered fiber ends are discussed above with respect to output beam steering (e.g., for data transmission or directed energy), these principles are also applicable to receiving. For example, through phased array processing in which phase offsets are applied on the receiving end, as well as through physical tilting of the tapered fiber ends, the directional sensitivity of a photonic antenna array acting as a receiver may be adjusted.
As mentioned above, exemplary embodiments of the present application may utilize an “adiabatic” or near-adiabatic taper which provides for a gentle enough slope that provides high efficiency through the taper (i.e., conserving brightness by avoiding undesirable scattering and back-reflections). A tapered fiber may be considered adiabatic if the taper angle is small enough such that there is negligible power coupling from the fundamental mode to higher-order modes. The following provides an example of adiabaticity criteria for delineating such conditions. The delineation angle Ω(r) as a function of the local taper radius r is given by the following length-scale criterion:
Ω(r)=r/2π(β1(r)−β2(r))
where β1(r) and β2(r) are the propagation constants of the fundamental (HE11) and the first excited (HE12) modes, respectively. If the local taper angle θ(r) is much smaller than Ω(r), the mode coupling is negligible and the fundamental mode propagates adiabatically. An adiabaticity factor F(>0) can be used to express this condition as follows:
θ(r)<FΩ(r)
Smaller F values lead to reduced mode coupling.
When this criterion is satisfied, ultra low loss tapers of almost any size core diameter can be created.
In the exponential tapered profile of the graph of
Exemplary embodiments of photonic antenna arrays discussed herein, as well as systems incorporating such photonic antenna arrays, are usable in a wide variety of different applications. For example, as a receiver, photonic antenna arrays of exemplary embodiments of the present application may be used in ultra-lightweight astronomical telescopes that can be used in space with fiber photonic signal processing. To provide another example, photonic antenna arrays of exemplary embodiments of the present application may be used as transmitters, receivers, and/or transceivers in large networks of optical communications crosslink networks for global communications and deep space coverage, such as large-scale satellite networks with satellites numbering in the thousands. There are also other applications of photonic antenna arrays of exemplary embodiments of the present application, such as for scanning, range-finding, directed energy, light detection and ranging (LIDAR), jamming and multi-beam applications, as well as for high peak power lasers on the petawatt scale. Further, because collimating lenses and gimballed telescopes are not needed with respect to photonic arrays of exemplary embodiments of the present application, greatly simplified construction of such systems can be achieved.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Claims
1. A photonic antenna array, comprising:
- a plurality of tapered fiber ends, wherein each tapered fiber end of the plurality of tapered fiber ends corresponds to a respective fiber of a plurality of fibers; and
- a support plate, wherein a portion of each of the plurality of fibers is run through the support plate;
- wherein a fiber core diameter at a tapered end point of a respective tapered fiber end of the plurality of tapered fiber ends has a first diameter, wherein a fiber core diameter at a non-tapered portion of the respective fiber corresponding to the respective tapered fiber end has a second diameter, and wherein the first diameter is smaller than the second diameter; and
- wherein the respective tapered fiber end is configured to provide a mode field diameter larger than a diameter of the non-tapered portion of the respective fiber corresponding to the respective tapered fiber end.
2. The photonic antenna array according to claim 1, wherein the respective tapered fiber end comprises an adiabatic taper from the second diameter to the first diameter.
3. The photonic antenna array according to claim 1, wherein multiple tapered fiber ends of the plurality of tapered fiber ends are configured to provide overlapping mode fields.
4. The photonic antenna array according to claim 3, wherein the overlapping mode fields each comprise collimated light, and the collimated light is coherently combined in overlapping areas of the overlapping mode fields.
5. The photonic antenna array according to claim 1, further comprising:
- a plurality of positioners, wherein each positioner is configured to actuate a respective tapered fiber end of the plurality of tapered fiber ends.
6. The photonic antenna array according to claim 5, wherein a respective positioner of the plurality of positioners comprises a tilt transducer configured to tilt the respective tapered fiber end corresponding to the respective positioner.
7. The photonic antenna array according to claim 5, wherein a respective positioner of the plurality of positioners comprises a piston transducer configured to provide a piston motion along a direction of propagation of the respective fiber corresponding to the respective positioner.
8. The photonic antenna array according to claim 1, wherein the plurality of tapered fiber ends are arranged in a two-dimensional array.
9. The photonic antenna array according to claim 1, wherein the photonic antenna array is configured to provide phased array-based beam steering based on the plurality of tapered fiber ends outputting beams that have relative phase offsets.
10. The photonic antenna array according to claim 1, wherein the second diameter is less than 5 μm.
11. The photonic antenna array according to claim 10, wherein the second diameter is less than 1 μm.
12. The photonic antenna array according to claim 1, further comprising:
- an index material, wherein the index material encapsulates the plurality of tapered fiber ends.
13. The photonic antenna array according to claim 12, wherein the index material has an index of refraction (n) greater than 1.
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Type: Grant
Filed: Dec 6, 2019
Date of Patent: Feb 14, 2023
Patent Publication Number: 20200183086
Assignee: OPTICAL ENGINES, INC. (Colorado Springs, CO)
Inventors: Donald Lee Sipes, Jr. (Colorado Springs, CO), Jason D. Tafoya (Colorado Springs, CO), Daniel Scott Schulz (Colorado Springs, CO)
Primary Examiner: Li Liu
Application Number: 16/705,912
International Classification: G02B 6/26 (20060101); H04B 10/112 (20130101); F21V 8/00 (20060101); H01Q 21/06 (20060101); H04B 10/118 (20130101); H04B 10/50 (20130101);
